We all know that what we experience is real. As real as the air that you cannot see, or the electrons that can be in two places at once, or the light that acts like a particle and a wave, but also brings life into being, and subsequently can/will take it away.

He is trying to bait you into an argument that cannot be won. Like the atheists who tell you to prove Jesus was real. Or Muhammad was a prophet. Or explaining "dark letter". Or even the devil.

We know what we experience. They don't because they don't want to experience a life like that. I think its scares the living shit out of them to think there is more to us, and the everything around us, than what science can presently be allowed to explain. Just live and let live. He will see it in time, or he won't. It makes no difference in our lives that he doesn't right now.